1. Field of the Invention
The invention relates to motion detection devices used in conjunction with video surveillance devices and to more particular to devices for detecting motion from an image on a video surveillance monitor.
2. Background Art
Video surveillance devices are commonly used for many applications in which the primary reason for the surveillance is to detect unauthorized activity such as the unauthorized opening of a doorway or other unauthorized activity. Basically, a monitoring camera is required for each area to be monitored and is typically connected by means of a cable to a dedicated monitor. In large installations, a single watch person is often responsible for observing a number of monitors in a single location. Alarm devices are known which alert the watch person to activity in an area under surveillance. The known devices are inserted in the transmission cable between a camera and a monitor and, by means of a processing of the electronic signals transmitted from the camera to the monitor, detect changes in the signals which are representative of changes in light intensity. Changes in light intensity are interpreted as movement in the area covered by the camera. Control circuitry allows the observer to designate an area of the field of view of the camera as the area to be analyzed by the alarm device. The alarm device generates an alarm, e.g. an audible alarm, when the analyzed signals indicate that a change in light intensity has occurred in the area under observation.
A disadvantage of prior art alarm devices, relying upon interpretation of electrical signals transmitted by the camera, is that the device must be inserted in the cable extending between the camera and the monitor. The installation must be done by skilled technicians and is therefore typically a permanent installation. A further disadvantage of the prior art units is the expensive circuitry required for analysis of the complex video signal transmitted between the camera and the monitor. The prior art unit typically requires monitoring system nobs on a control panel accessible to the watch person to allow the watch person to select various areas of the picture to be monitored.
The requirements for motion detection in various areas vary from time to time and may well vary between different time periods in the same day. It is therefore desirable to have a motion detector, that can be selectively activated for each monitored location. However, the expense of permanently installing a unit such as known in the prior art for each camera installation is expensive. Furthermore, the equipment often is used for only a small portion of the total time that the camera is activated.